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Finish on Square Tubing -

I'm working on a set of tables, and using 1 inch square tubing. I've cleaned the oil off of the metal, but it's still left with a sort of smoke grey color. I've used a heavy wire-brush on my 7" grinder to remove this finish, but it is real difficult. I heard a lot of comments about mill scale, and was wondering if this is this smoke grey color on the metal, or if it's just a different chemical sprayed on the tube to prevent rusting.

Any good suggestions for removal? Other than the tedious wire brushing - it sticks real well!

Thanks

I'll submit the finished pictures in the projects section. I'm going to remove the color, as I want the shiny silver color, that I'm spraying with clear finish to keep from tarnishing/rusting. However, I've seen some nice metal colorings now. Might post that as a separate question under projects.

Some mill scale can be quite difficult to remove. I've found that wire brushes sometimes only burnish the scale.
You may want to try a flap disc (careful, they can be aggressive) or a non woven abrasive like a 3-M type scotch brite discs. If a polished steel look is what you want the scotch-brite discs work good. For a tough clear finish try 'PERMALAC'.

I believe he is just talking about the regular grey Mill Finish. If you haven't welded it up yet, be sure you pay attention to the seams on the square tubing, so you can position the seam to the rear. The seams usually have somewhat of an indentation along them, which you will discover when you start cleaning and polishing them.

Removing scale - flap disk

I've used a flap disk on the metal, with mixed results. The disk has a hard time getting into the center of the dimple on the tube (especially on the welded side), unless you really grind quite a bit of the edges away. Also, even the 120 grit leaves quite a few scratches.
Even the wire brush on the big grinder leaves scratches, but not as severe.

The one thing I found that is really nice if you want a real smooth finish is a polishing/grinding disk at my LWS, which really polishes the metal after being wire brushed. It almost makes the metal look like it's been chromed - however, it does wear away fairly quick - I need to get another couple for the second piece of my project, and take a picture show everyone. They have 2 levels, one is a orange color, and the other is green - but they aren't Scotch Brite pads. These are fairly smooth - but firm, with just a little abrasiveness. I haven't seen these grinder disks anywhere else.

Interested

I use a lot of tube and usually spray color. If the coating is difficult to get off, I scuff everything with 120 before prime/paint and it sticks really well. I'm always interested in other types of finish though, and would like to know the type of disc you mentioned.

Finishing pads for steel

After mentioning the pads at the LSW, something like 200 and 400 grit, but they don't say, I found something that fits my needs better. The problem I had using the 200 grit to remove the deep 120 flapdisk scratches, and it burns up the disk very quickly. I've just found at Harbor Freight (item # 65287) a set of 5 of abrasive pads, with steps of grit of 40, 80, 220, 400, 600 - they even label these as polishing disks. This 40 grit is nothing like a 40 grit flap disk - it is a good follow-up to a 120 flap disk, and it will remove the those scratches leaving only fairly fine scratches which you can remove with the 80 grit, and then the next one and so on, and really, I don't even see much need for the 600 grit. The 400 grit disks will leave the metal 'chrome like shiny', so I'm really pleased with this set of Disks - I would like the quality to be a little better to last a little longer, but so far it's the only place I've seen the lower grit numbers that give this type of finish.

The Harbor Freight webpage describes them for stone or metal, but I haven't seen anything like this anywhere else - probably might be found at a supplier of consumables for the granite counter/stone cutting trade?
This set says dry only, where I think they do granite and stone with wet processes.